1. Field of the Invention
The present invention relates to tubular body cannisters fabricated of paperboard or a laminate including paper having independently applied end closure caps.
2. Description of the Prior Art
Tubular body cannisters made from paperboard and paper inclusive laminates are frequently terminated with end closures formed of metal, plastic or paperboard. These end closures may be a simple plug structure or a more complex shape having a hat section channel around the closure perimeter to receive the terminal annulus of the cannister tube.
Many means and techniques have been and are presently being used to seal and secure such end cap closures to a cannister tube body. One of the more successful techniques has been to apply a thin bead of hot melt adhesive around the cannister tube interior near the tube end. When pressed into position, the end cap channel or plug portion wipes across the adhesive bead thereby providing a continuous caulking seal and structural joint bond.
Although simple in theory, the hot melt bead technique for securing and sealing an end cap to a cannister tube is difficult to execute and correspondingly unreliable due to variations in the hot melt bead thickness section.
The bead is jetted onto the cannister tube surface by a fluid nozzle supplied by a pressured fluid source of hot melt. The actual adhesive jetting interval is about 200 milliseconds out of a 500 milliseconds cycle. Within another 200 milliseconds, the preceding capped cannister is removed from the jet station and replaced by an uncapped tube. During the removal and replacement interval, adhesive flow to the jet nozzle is terminated while constant displacement volume from a gear pump is accommodated through a circulation loop past a pressure regulation valve.
Although the objective of the pressure regulation valve is to maintain constant pressure at the junction of the nozzle spur with the circulation loop, this objective is not in fact accomplished due to the rapid cycle times involved and the mechanical mass characteristics of the pressure regulation valve. Pressure levels at the conduit junction vary quite considerably. As a consequence of such pressure variations, the volumetric quantity of adhesive jetted from the nozzle varies correspondingly. An adhesive bead on the cannister surface of irregular sectional area is the result.
It is, therefore, an objective of the present invention to teach an adhesive jetting method that will deliver an adhesive bead to a cannister surface of substantially uniform sectional area.
Another object of the present invention is to teach the construction of an adhesive delivery system that will maintain a substantially constant pressure at a conduit junction of a nozzle spur with a circulation loop.